This invention relates to a unit for measuring shape defects of a part, and a measuring process used in such a unit.
In the case of a digitized left surface, a body part of a motor vehicle, for example, any point of this surface can be calculated as coordinates X, Y, Z in an orthonormed reference frame. The actual shape of the part, after production, differs slightly from the theoretical shape. It is therefore necessary to know the deviations existing between the theoretical shape and the actual shape, to modify the production conditions.
The known measuring units comprise a ground plane installation, called a surface plate below, on which is installed a presentation unit receiving the part to be measured, a three-dimensional measuring machine and a computer. The machine is equipped with a trigger sensor mounted on a head and three counters quantifying the displacements of the sensor along the three axes.
The process used in such known measuring units consists in placing the part on its display unit, then in sensing this part along a number of previously determined points. The operator manually displaces the sensor from point to point and at each point brings the sensor into contact on the part. The sensor then triggers the acquisition by the computer of the three values read by the counters. A comparison of the values read and processed by the computer with the theoretical values quantifies the defect of shape at a pinpointed location.
This measuring process is slow, because it is necessary to place the sensor straight above each predetermined point and to make a contact with the part to perform the acquisition of the three coordinates.
This process makes the analysis of the defects inaccurate, because the number of measured points is small. The increase of the number of measured points would require a long and costly preparation (range) and use.